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Biomedical subjects

R R Price

Publications and source records attributed to R R Price.

88 records · Page 5Linked to original sources
PubMed1975

Body composition in morbidly obese patients before and after jejunoileal bypass.

A clinical and body compositional study has been made of 150 patients with morbid obesity and their responses to four different dimensional alterations of jejunoileal bypass. Total body potassium was estimated by measuring 40K with the whole body counter and total body water by tritiated water dilution. Body compositional data derived from these measurements were compared in the 4 groups during followup periods up to 4 years and related to clinical results. Initially, patients were two or more times overweight due to excess (60 to 65%) body fat and increased hydration (21%) of lean tissues. The 80 end-to-end jejunoileal bypass procedures of Groups 3 and 4 (30 cm jejunum to 15 or 20 cm ileum) had better weight losses and clinical results in followup were rated "good" in 60% and 81% respectively. These results were accompanied by a greater degree of improvement in body composition than was observed in the other groups under study.

Adolescent↗
PubMedDate not supplied

In vivo fluorine-19 MR imaging: relaxation enhancement with Gd-DTPA.

The lack of a naturally occurring background signal from fluorine in magnetic resonance (MR) imaging makes fluorinated compounds potentially attractive candidates for tissue-specific MR contrast agents. Problems associated with the in vivo use of fluorinated compounds are toxicity, which limits the amount of agent that can be used; multiple resonance lines; and an excessively long T1, which leads to long sequence TRs and consequently long imaging times. Many fluorinated agents also possess complex MR spectra that result in chemical shift artifacts if not corrected. The authors demonstrate the use of an extracellular fluorinated agent with a single MR peak for selective imaging of a brain abscess in an animal model and show that the image signal per unit of acquisition time can be enhanced through the use of a T1 relaxation agent, gadolinium diethylenetriamine-pentaacetic acid (DTPA). Trifluoromethylsulfonate was administered at a fluorine-19 dose of 4 mmol/kg, and fluorine images of the induced abscess were acquired before and after the injection of a standard dose of Gd-DTPA (0.1 mmol/kg); non-section-selected projection images were used. Typical imaging times were less than 5 minutes. The signal enhancement factor achieved was approximately four (4.0 +/- 0.8) with use of a 500/12 (TR msec/TE msec) spin-echo sequence.

Animals↗
PubMedDate not supplied

Diffusion imaging with the MP-RAGE sequence.

Diffusion-weighted magnetic resonance (MR) images obtained with conventional spin-echo techniques are known to be sensitive to subject motion because of long image acquisition times. To reduce the acquisition time, use of a magnetization-prepared rapid gradient-echo (MP-RAGE) sequence modified for diffusion sensitivity was studied. In this sequence, a preparation phase with a 90 degrees-180 degrees-90 degrees pulse train is used to sensitize the magnetization to diffusion. Centric-ordered phase encoding, short TRs (5.2-6.5 msec), and small flip angles (5 degrees-8 degrees) are necessary to minimize saturation effects from tissues with short relaxation times. Phantom studies with various concentrations of copper sulfate (T1 ranging from 2,459 to 90 msec) were performed to validate that the diffusion-weighted signal obtained with the MP-RAGE sequence was independent of relaxation time. Diffusion-weighted images of water, isopropyl alcohol, and acetone were acquired to confirm the accuracy of measured diffusion coefficients. Brain images of healthy normal volunteers were obtained to demonstrate motion insensitivity and general image quality of the technique. The results indicate that accurate diffusion-weighted images can be obtained with a diffusion-weighted MP-RAGE sequence, with imaging times of about 1 second.

1-Propanol↗
PubMedDate not supplied

In-vitro release characteristics of tetracycline HCl, khellin and nicotinamide adenine dineculeotide from halloysite; a cylindrical mineral.

The use of halloysite clay as a low cost alternative to more traditional microencapsulation systems is reported. Halloysite is an alumino-silicate clay which demonstrates a predominately cylindrical geometry, uniquely characterized by a hollow core or series of voids with diameters ranging from 16-50 nm. These nanoscale-to-mesoscale microcylinders are capable of entrapping active agents within the core lumen as well as within any void spaces contained in the multilayered walls of the cylinder. Some of the active agents associated with the clay are also bound to the external surfaces of the clay. Delivery of the active agent is first by desorption of the active agent from the exterior surfaces and exposed ends of the microcylinders, and is followed by a second more prolonged phase dominated by pore diffusion from the ends of the cylinders. Halloysite is capable of retaining and releasing a range of active ingredients. Both hydrophilic and hydrophobic agents may be entrapped following appropriate pre-treatment of the clay to render it lipophilic. Here, a unique low cost alternative microcylindrical delivery system: the clay mineral halloysite, is investigated.

Aluminum Silicates↗
PubMedDate not supplied

Volumetric determination of placental and uterine growth relationships from B-mode ultrasound by serial area-volume determinations.

Serial area-volume determinations may be made from B-mode ultrasonography. Multiple sonographic sections are taken through a structure of interest. The area of the structure of interest is determined on each sonographic section by a form of planimetry and multiplied by the step-interval to obtain the volume of the structure of interest between sonographic sections. The total volume of the structure of interest is the sum of the individual volumes. The volume is computed from both transverse and longitudinal images and an average obtained for improved accuracy. Total intrauterine volume and placental volume were determined by the serial area-volume method in 63 normal patients and the results were analyzed. Placental and total intrauterine volumes were also determined for five cases of intrauterine growth retardation. Although there is some error in the serial area-volume method, the initial evaluation of five cases with intrauterine growth retardation suggests a greater precision and accuracy than volume estimates based on prolate ellipsoid geometry. Placental volume may provide an acceptable parameter to screen for intrauterine growth retardation.

Female↗
PubMedDate not supplied

Digital image motion correction by spatial warp methods.

A technique for correction of motion between images which are obtained in high-speed digital subtraction or cine angiographic acquisitions is being tested. The method is based on the application of quadratic polynomial equations which transform one image so that it matches a reference image. Images which have been processed in this manner can be summed to improve the signal-to-noise ratios over individual images. The technique for motion correction currently being tested uses operator interaction to establish the appropriate polynomial transformation. An operator selects fiducial (reference) points on an image which will be the reference. Then he selects the corresponding fiducial points on the image to be processed. The algorithm calculates the coefficients of a pair of quadratic polynomial equations and applies them to each pixel in the image. Results demonstrate the application of the technique in phantoms and in digitized cine angiograms.

Angiography↗
PubMedDate not supplied

The AAPM/RSNA physics tutorial for residents. MR imaging safety considerations. Radiological Society of North America.

Experience and research over the past decade have demonstrated that diagnostic magnetic resonance (MR) imaging is a biologically safe imaging modality. Specifically, there is currently no convincing evidence that there is any long-term or irreversible biologic effects associated with the radiation and magnetic fields used in MR imaging, specifically radio-frequency (RF) radiation, static magnetic fields, and time-varying gradient fields. However, numerous hazards of MR imaging do exist that can cause severe injuries or even death. These hazards are primarily the result of (a) strong magnetic fields and the strong force that they exert on ferromagnetic objects brought into their influence, including interference with electronic devices such as pacemakers and other implanted electronic devices, and (b) RF burns resulting from inadvertently induced currents in conductive loops placed on the patient's skin surface (eg, electrocardiographic leads and other monitoring devices). Other potential concerns are peripheral nerve stimulation resulting from rapidly switched gradients and auditory noise levels. Establishing a complete and coordinated educational program for all MR imaging facility personnel and conducting effective screening and preparation of patients scheduled for MR imaging procedures are essential to avoid accidents and RF burns and to maintain a safe MR imaging facility.

Accident Prevention↗
PubMedDate not supplied

Entrapment and release characteristics of 2-methoxynaphthalene from cylindrical microstructures formed from phospholipids.

Many natural products that exhibit biocidal activity have poor solubility in water. In order to explore the prolonged delivery of these compounds from microtubules we have utilized 2-methoxynaphthalene as a model to elucidate release characteristics of hydrophobic compounds entrapped in microtubules by spectrophotometric absorbance at 255 nm. Entrapment of this compound in microcylinders was accomplished by addition of 2-methoxynaphthalene to a water-soluble epoxy, or entrapment of the neat compound. Variation of the release rate is possible for 2-methoxynaphthalene based on the mode of entrapment and by variations in the methods used to immobilize the compound within the microcylinders. Unlike conventional microencapsulation techniques which require inclusion of the active agent at the time of formation, the use of microcylinders allows for the inclusion of a variety of active agents and the tailoring of release characteristics after their formation. We report the results of in vitro release rates of 2-methoxynaphthalene from a static diffusion system designed to explore release of hydrophobic compounds into an aqueous environment.

Capsules↗
PubMedDate not supplied

Emulsification preparation of calcium alginate beads in the presence of sequesterant.

A biocompatible emulsification method has been developed for microencapsulation of live cells and enzymes within a calcium alginate matrix. Fabrication of alginate beads was achieved by premixing a sequestering agent (sodium polyphosphate) and the calcium source (calcium sulphate) with the hydrogel monomer prior to the introduction to the oil phase. The competition between the sequesterant and sodium alginate in binding the available calcium ions results in a slowing down of the rate of polymerization and thereby lead to a successful calcium alginate bead formation. The mean diameter of the fabricated beads may be easily controlled by employing soy bean lecithin as an emulsifier. The polymerization time in this process may vary between 3 and 35 min depending on the ratio of sequesterant to that of calcium source at constant sodium alginate concentration. This preparation method avoids the use of pH extremes at all times and therefore is particularly suitable for encapsulating pH-sensitive cells and enzymes.

Alginates↗
PubMedDate not supplied

NMR: state of the art in medical imaging.

The future of NMR imaging in medicine seems bright. Absence of known biologic hazard, lack of moving parts, and ability to measure multiple tissue parameters should make it the study of choice in many clinical situations, while its ability to create detailed tomographic images in any plane, with both anatomic detail and tissue specificity, should revolutionize diagnostic radiology. The additional information gained about metabolic processes in vivo may well change our entire understanding of health and disease.

Magnetic Resonance Spectroscopy↗